Gerard K. O’Neill, President, Space Studies Institute, 1990

The earliest acquisition of space resources should be the retention and maintenance in Earth orbit of discarded Space Shuttle external tanks. Currently, the tanks are brought to 99% of orbital energy, then are dumped back into the atmosphere, wasted. Each tank weighs considerably more than a maximum Shuttle payload, and its materials, mainly aluminum, are well known. The tanks are usable with almost no alteration as pressure shells for habitable working space (as was Skylab, which was built from an Apollo upper stage). The addition to an external tank of lightweight insulation is an undemanding job and would convert the tank into a long-term storage medium for propellants. Most Shuttle flights are volume-limited rather than weight limited. Therefore, each Shuttle flight could carry to such an orbital tank farm, at little cost, propellants not needed for that flight itself, which could be transferred to the long-term storage tank.

The uses of such stored propellants include maintaining or raising the orbits of space stations and tank farms, fueling scientific spacecraft destined for voyages to other planets, and, especially, fueling shuttle craft operating between relatively low-Earth orbit and orbit about the Moon.

Uses of external tank materials for construction include aluminum fabrication into structural beams, counterweights, gantries, storage warehouses, solar cell array backings, electrical conductors, and specialized pressure shells for space stations. In a cost effective space program, space stations should be fabricable at relatively short notice and at low cost from the ready reserve of well-understood materials available in orbit from stockpiled external tanks. The time scale for initial developmental trials in space of these techniques should be the early 1990s, for example, 1993.